Abstract : Voltage jump experiments to investigate the effect of the voltage jump section length were continued. In particular, a correlation between the optimum voltage jump section length and the gain parameter C was established. Investigations of velocity step tapers were resumed, and an optimum design two step velocity taper circuit was evaluated. Both the voltage jump and the velocity step taper techniques were combined for the first time. This resulted in higher conversion efficiencies (more than 50%) than were obtainable with either of the two methods alone. An upgraded large signal computer program for traveling-wave tubes was used to explore the capabilities of the voltage jump technique for a wide range of tube parameters. For these parameters, the expected efficiency improvement with a voltage jump circuit together with the design data for the optimum voltage jump section length are given. The best operating conditions for the driver section are shown as well as data on the gain, launching loss, and gain compression in the driver section. The limitations of collector depression due to the energy spread of the spent beam have also been investigated. (Author)